Imaging optical system and optical apparatus using the same

ABSTRACT

An imaging optical system has a variable magnification optical system. The variable magnification optical system includes, in order from the object side, a first lens unit with positive refractive power, a second lens unit with positive refractive power, a third lens unit with negative refractive power, a fourth lens unit with positive refractive power, and an aperture stop interposed between the third lens unit and the fourth lens unit. The variable magnification optical system changes an imaging magnification while keeping an object-to-image distance constant. The imaging magnification is changed by varying spacing between the first lens unit and the second lens unit, spacing between the second lens unit and the third lens unit, and spacing between the third lens unit and the fourth lens unit. When the imaging magnification is changed, the imaging optical system satisfies the following conditions in at least one variable magnification state:  
     | En|/L   &gt;0.4    
     | Ex/|L   /β|&gt;0.4    
     where En is a distance from a first lens surface on the object side of the variable magnification optical system to the entrance pupil of the imaging optical system, L is the object-to-image distance of the imaging optical system, Ex is a distance from the most image-side lens surface of the variable magnification optical system to the exit pupil of the imaging optical system, and β is the magnification of the entire system of the imaging optical system.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a variable magnification lens which iscapable of changing an imaging magnification in accordance with thepurpose of use and an optical system which is capable of photographingan image recorded by a film at a magnification most suitable for thefilm, and to an optical apparatus, such as an image transformingapparatus, using this optical system.

[0003] 2. Description of Related Art

[0004] Imaging optical systems which are designed to be both-sidetelecentric and to change the imaging magnification have been proposed,for example, by Japanese Patent Kokai No. 2001-27726 and Japanese PatentNo. 2731481.

[0005] The optical system set forth in Kokai No. 2001-27726 includes, inorder from the object side, the first lens unit with positive refractivepower, the second lens unit with positive refractive power, the thirdlens unit with negative refractive power, and the fourth lens unit withpositive refractive power. This optical system is thus constructed to beboth-side telecentric and to change the imaging magnification.

[0006] The optical system set forth in Patent No. 2731481 includes, inorder from the object side, the first lens unit with positive refractivepower, the second lens unit with negative refractive power, and thethird lens unit with positive refractive power. This optical system isthus constructed to be both-side telecentric and to change the imagingmagnification while keeping an object-to-image distance constant.

SUMMARY OF THE INVENTION

[0007] The imaging optical system of the present invention includes avariable magnification optical system comprising, in order from theobject side toward the image side, a first lens unit with positiverefractive power, a second lens unit with positive refractive power, athird lens unit with negative refractive power, a fourth lens unit withpositive refractive power, and an aperture stop interposed between thethird lens unit and the fourth lens unit. The variable magnificationoptical system changes an imaging magnification while keeping anobject-to-image distance constant. The imaging magnification is changedby varying spacing between the first lens unit and the second lens unit,spacing between the second lens unit and the third lens unit, andspacing between the third lens unit and the fourth lens unit. When theimaging magnification is changed, the imaging optical system satisfiesthe following conditions in at least one variable magnification state:

|En/L>0.4

|Ex|/|L/β|>0.4

[0008] where En is a distance from a first lens surface on the objectside of the variable magnification optical system to the entrance pupilof the imaging optical system, L is the object-to-image distance of theimaging optical system, Ex is a distance from the most image-side lenssurface of the variable magnification optical system to the exit pupilof the imaging optical system, and β is the magnification of the entiresystem of the imaging optical system.

[0009] The imaging optical system of the present invention preferablysatisfies the following conditions:

1.0<MAXFNO<8.0

|ΔFNO/Δβ|<5

[0010] where MAXFNO is the smallest object-side F-number where theimaging magnification of the imaging optical system is changed, ΔFNO isa difference between the object-side F-number at the minimummagnification and the object-side F-number at the maximum magnificationin the entire system of the imaging optical system, and Δβ is adifference between the minimum magnification and the maximummagnification in the entire system of the imaging optical system.

[0011] The imaging optical system of the present invention preferablysatisfies the following condition:

0.6<|(R3f+R3b)/(R3f−R3b)|<5.0

[0012] where R3f is the radius of curvature of the most object-sidesurface of the third lens unit and R3b is the radius of curvature of themost image-side surface of the third lens unit.

[0013] The imaging optical system of the present invention is preferablyconstructed so that the most object-side lens of the first lens unit haspositive refractive power.

[0014] The imaging optical system of the present invention is preferablyconstructed so that the first lens unit includes, in order from theobject side, a lens with positive refractive power, a lens with negativerefractive power, and a lens with positive refractive power.

[0015] The imaging optical system of the present invention is preferablyconstructed so that the third lens unit includes at least two meniscuslenses, each with a convex surface directed toward the object side.

[0016] The imaging optical system of the present invention is preferablyconstructed so that the third lens unit includes two meniscus lenses,each with negative refractive power, and one meniscus lens with positiverefractive power.

[0017] In the present invention, an optical apparatus using the imagingoptical system of the present invention is provided.

[0018] According to the present invention, the imaging optical system inwhich even when the imaging magnification is changed, theobject-to-image distance remains unchanged and the fluctuation of theF-number is minimized, and the optical apparatus using the imagingoptical system can be provided.

[0019] These and other features and advantages of the present inventionwill become apparent from the following detailed description of thepreferred embodiments when taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIGS. 1A, 1B, and 1C are sectional views showing opticalarrangements, developed along the optical axis, at magnifications of0.3×, 0.4×, and 0.5×, respectively, of a first embodiment of the imagingoptical system according to the present invention;

[0021]FIGS. 2A, 2B, and 2C are diagrams showing aberrationcharacteristics in focusing at an imaging magnification of 0.4× of theimaging optical system in the first embodiment;

[0022]FIGS. 3A, 3B, and 3C are sectional views showing opticalarrangements, developed along the optical axis, at magnifications of0.3×, 0.4×, and 0.5×, respectively, of a second embodiment of theimaging optical system according to the present invention;

[0023]FIGS. 4A, 4B, and 4C are diagrams showing aberrationcharacteristics in focusing at an imaging magnification of 0.4× of theimaging optical system in the second embodiment;

[0024]FIGS. 5A, 5B, and 5C are sectional views showing opticalarrangements, developed along the optical axis, at magnifications of0.3×, 0.4×, and 0.5×, respectively, of a third embodiment of the imagingoptical system according to the present invention;

[0025]FIGS. 6A, 6B, and 6C are diagrams showing aberrationcharacteristics in focusing at an imaging magnification of 0.4× of theimaging optical system in the third embodiment;

[0026]FIGS. 7A, 7B, and 7C are sectional views showing opticalarrangements, developed along the optical axis, at magnifications of0.3×, 0.4×, and 0.5×, respectively, of a fourth embodiment of theimaging optical system according to the present invention;

[0027]FIGS. 8A, 8B, and 8C are diagrams showing aberrationcharacteristics in focusing at an imaging magnification of 0.4× of theimaging optical system in the fourth embodiment;

[0028]FIGS. 9A, 9B, and 9C are sectional views showing opticalarrangements, developed along the optical axis, at magnifications of0.3×, 0.4×, and 0.5×, respectively, of a fifth embodiment of the imagingoptical system according to the present invention;

[0029]FIGS. 10A, 10B, and 10C. are diagrams showing aberrationcharacteristics in focusing at an imaging magnification of 0.4× of theimaging optical system in the fifth embodiment;

[0030]FIGS. 11A, 11B, and 11C are sectional views showing opticalarrangements, developed along the optical axis, at magnifications of0.3×, 0.4×, and 0.5×, respectively, of a sixth embodiment of the imagingoptical system according to the present invention;

[0031]FIGS. 12A, 12B, and 12C are diagrams showing aberrationcharacteristics in focusing at an imaging magnification of 0.4× of theimaging optical system in the sixth embodiment;

[0032]FIGS. 13A, 13B, and 13C are sectional views showing opticalarrangements, developed along the optical axis, at magnifications of0.3×, 0.4×, and 0.5×, respectively, of a seventh embodiment of theimaging optical system according to the present invention;

[0033]FIGS. 14A, 14B, and 14C are diagrams showing aberrationcharacteristics in focusing at an imaging magnification of 0.4× of theimaging optical system in the seventh embodiment;

[0034]FIGS. 15A, 15B, and 15C are sectional views showing opticalarrangements, developed along the optical axis, at magnifications of0.3×, 0.4×, and 0.5×, respectively, of an eighth embodiment of theimaging optical system according to the present invention;

[0035]FIGS. 16A, 16B, and 16C are diagrams showing aberrationcharacteristics in focusing at an imaging magnification of 0.4× of theimaging optical system in the eighth embodiment;

[0036]FIGS. 17A, 17B, and 17C are sectional views showing opticalarrangements, developed along the optical axis, at magnifications of0.3×, 0.4×, and 0.5×, respectively, of a ninth embodiment of the imagingoptical system according to the present invention;

[0037]FIGS. 18A, 18B, and 18C are diagrams showing aberrationcharacteristics in focusing at an imaging magnification of 0.4× of theimaging optical system in the ninth embodiment;

[0038]FIG. 19 is a conceptual view showing an embodiment of a telecineapparatus using the imaging optical system of the present invention; and

[0039]FIG. 20 is a view showing schematically an embodiment of a heightmeasuring apparatus using the imaging optical system of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] Before undertaking the description of the embodiments, thefunction and effect of the present invention will be explained.

[0041] In the imaging optical system of the present invention, asdescribed above, the variable magnification optical system includes fourlens units with positive, positive, negative, and positive refractivepowers. Ahead of (or on the object side of) the stop, the first lensunit with positive refractive power, the second lens unit with positiverefractive power, and the third lens unit with negative refractive powerare arranged so that the whole of these lens units constitutes a lenssystem with positive refractive power. The fourth lens unit locatedbehind (or on the image side of) the stop constitutes a lens system withpositive refractive power. The aperture stop is interposed between thethird lens unit and the fourth lens unit.

[0042] The imaging optical system of the present invention is designedto change the imaging magnification while keeping the object-to-imagedistance constant. That is, the imaging optical system of the presentinvention is an optical system in which a conjugate length is fixed.

[0043] The imaging optical system of the present invention isconstructed so that when the imaging magnification is changed, theimaging optical system satisfies the following conditions in at leastone variable magnification state and is both-side telecentric:

|En|/L>0.4  (1)

|Ex|/|L/β|>0.4  (2)

[0044] where En is a distance from a first lens surface on the objectside of the variable magnification optical system to the entrance pupilof the imaging optical system, L is the object-to-image distance of theimaging optical system, Ex is a distance from the most image-side lenssurface of the variable magnification optical system to the exit pupilof the imaging optical system, and β is the magnification of the entiresystem of the imaging optical system.

[0045] The imaging optical system of the present invention isconstructed so that the stop is located at the focal position of thelens system made up of the first to third lens units lying on the objectside of the stop. By this arrangement, the entrance pupil which is theimage of the stop is projected at infinity. As a result, the imagingoptical system of the present invention constitutes an object-sidetelecentric optical system.

[0046] Further, the imaging optical system of the present invention isconstructed so that the stop is located at the focal position of thelens system of the fourth lens unit lying on the image side of the stop.By this arrangement, the exit pupil which is the image of the stop isprojected at infinity. As a result, the imaging optical system of thepresent invention also constitutes an image-side telecentric opticalsystem.

[0047] In the imaging optical system of the present inventionconstructed as mentioned above, the role of a multi-variator is allottedto each of the second lens unit with positive refractive power and thethird lens unit with negative refractive power. Whereby, a synthesizedfocal length of the first to third lens units located on the object sideof the stop can be changed.

[0048] Still further, the imaging optical system of the presentinvention is constructed so that the stop is interposed between thethird lens unit and the fourth lens unit. The fourth lens unit locatedon the image side of the stop has no variable magnification function.Even when the imaging magnification is changed, the shift of theposition of the stop is suppressed as far as possible so that theposition of the stop remains practically unchanged. An arrangement isthus made such that the stop is always located in the proximity of thefocal position of the fourth lens unit, and thereby the imaging opticalsystem is capable of changing the imaging magnification whilemaintaining the telecentric characteristic and the F-number on the exitside. However, in order to maintain the object-side telecentriccharacteristic and fix the conjugate length while keeping the F-numberconstant when the imaging magnification is changed, it is necessary tosatisfy conditions described below. First, even in the magnificationchange, the stop must be located at the synthesized focal position ofthe first to third lens units lying on the object side of the stop.Second, even in the magnification change, a distance from an objectsurface to a stop surface must be kept nearly constant.

[0049] In the lens arrangement of positive, negative, and positiverefractive powers, if the first lens unit is divided into two lens unitswith positive and negative refractive powers, the balance between therefractive powers will be destroyed. Consequently, chromatic aberrationof magnification and distortion will be increased. As in the presentinvention, when the first lens unit is divided into two lens units withpositive and positive refractive powers and the optical system isconstructed with four lens units with positive, positive, negative, andpositive refractive powers, the amount of the production of aberrationcan be minimized.

[0050] In the both-side telecentric optical system, even when themagnification is changed, an off-axis ray of light at the position ofthe stop is nearly parallel to the optical axis. On the image side ofthe stop, only the fourth lens unit is located, and it is not moved,thus making the focal length constant. Hence, when the magnification ischanged, the fluctuation of the image-side F-number is minimized, and itis not necessary to adjust the brightness of a camera even in this case.

[0051] When the object-side telecentric optical system is constructedlike the imaging optical system of the present invention, the followingadvantages are obtained. To explain this, a telecine apparatus (a motionpicture film scanner) is cited as an example. The telecine apparatus isadapted to digitize the motion picture film. The telecine apparatus isconstructed so that the film is illuminated by an illumination opticalsystem and an image is formed by a solid-state image sensor, such as aCCD, through the imaging optical system.

[0052] However, when the imaging optical system of the telecineapparatus is constructed to be object-side telecentric like the imagingoptical system of the present invention, matching of the pupil of theillumination system with the imaging system is facilitated, and a lossof the amount of light is reduced. Moreover, a change in magnificationon an image plane, caused by the disturbance of flatness of the film,can be kept to a minimum.

[0053] When the image-side telecentric optical system is constructedlike the imaging optical system of the present invention, the followingadvantages are obtained. To explain this, a so-called multi-imagercamera using image sensors in accordance with colors, such as RGB, iscited as an example. In this multi-imager camera, a color separationprism is generally used. This prism has a separation interference filmsplitting light in accordance with wavelength, namely a dichroic film,on its interface. If the exit pupil is located close to the image plane,the angle of incidence where a chief ray is incident on the interferencefilm will be changed in accordance with the position of an image pointon the image. Consequently, the optical path length of film thickness ischanged and a color separation characteristic is varied in accordancewith a field angle, bringing about different color reproducibility, thatis, causing color shading.

[0054] However, when the imaging optical system of the multi-imagercamera is constructed to be image-side telecentric like the imagingoptical system of the present invention, color shading can besuppressed.

[0055] Here, for example, it is assumed that the solid-image sensor,such as the CCD, is placed on the image side of the color separationprism. If the exit pupil is located close to the image plane, the chiefray is obliquely incident on a pixel. Thus, off-axis incident light ischiefly blocked by the structure of the CCD to decrease the amount oflight, and light other than that to enter an original light-receivingsection is incident. This brings about a state where a signal other thanoriginal information is output. That is, shading is caused.

[0056] However, when the image-side telecentric optical system isconstructed like the imaging optical system of the present invention,shading can be suppressed.

[0057] The imaging optical system of the present invention is alsoconstructed as the both-side telecentric optical system. Consequently,the imaging magnification can be practically determined by the ratiobetween the focal length of the lens units located on the object side ofthe stop and the focal length of the lens unit located on the image sideof the stop.

[0058] Spacings between individual lens units located on the object sideof the stop are changed so that the focal length of the lens units onthe object side of the stop is varied. Whereby, the imagingmagnification can be changed.

[0059] In the imaging optical system of the present invention, the firstlens unit has the positive refractive power, and the entrance pupilwhich is the image of the stop is projected at infinity. In doing so, achief ray on the object side of the first lens unit is refractedparallel to the optical axis and thereby the object-side telecentricoptical system can be realized.

[0060] In the imaging optical system of the present invention, thesecond lens unit has the positive refractive power and the third lensunit has the negative refractive power. By changing the spacing betweenthe second lens unit and the third lens unit, the synthesized focallength of the second and third lens units is varied. That is, the secondand third lens units are designed to function as a multi-variator. Thus,the second and third lens units are moved, and thereby the magnificationcan be optimally adjusted to the size of an object.

[0061] When the third lens unit is designed to have the negativerefractive power like the imaging optical system of the presentinvention, the Petzval sum is increased and an optical system which isfree of curvature of field can be realized.

[0062] The imaging optical system of the present invention is alsoconstructed so that the positive refractive power is imparted to thefourth lens unit and the exit pupil which is the image of the stop isprojected at infinity. Thus, the chief ray on the image side of thefourth lens unit is rendered parallel to the optical axis, and therebythe image-side telecentric optical system can be realized.

[0063] When the imaging optical system of the present invention providedwith the variable magnification function, mentioned above, is used toconstruct an optical apparatus, the following advantages are obtained.To explain this, for example, the telecine apparatus is cited asdescribed above. The telecine apparatus, in which a video camera isattached to a film photographing device, is constructed so that the filmimage is converted into a video signal, which is digitized.

[0064] On the other hand, motion picture films have a plurality ofstandards, and the size of the image section of the film varies witheach standard. For example, a 35 mm standard film measures 16(height)×21.95 (width) mm and a European wide film measures 11.9×21.95mm. In this way, the aspect ratio of the film varies according to thefilm standard. The dimension of the imaging surface of the CCD, forexample, in a ⅔″ CCD solid-state image sensor, is 5.4×9.6 mm. In orderto photograph an image through superfine pixels, it is desirable toacquire image information relative to the entire CCD imaging area. Forthis purpose, it becomes necessary to change the imaging magnificationin accordance with the film standard.

[0065] However, when the imaging optical system of the present inventionis used to construct the optical apparatus, the films of variousstandards can be digitized, for example, in the telecine apparatus. Inthis case, even when the imaging magnification is changed, the conjugatelength remains unchanged, and the magnification can be varied withlittle fluctuation in image-side F-number.

[0066] For example, when the imaging optical system of the presentinvention is used to construct the multi-imager camera, color shadingcaused by the color separation prism and shading of the CCD camera canbe suppressed. Moreover, the imaging magnification can be changed,without moving the camera, in accordance with the film standard and thesize of the object, and even when the magnification is changed, theadjustment of brightness is unnecessary.

[0067] In the imaging optical system of the present invention, in orderto obtain further both-side telecentricity, it is favorable that whenimaging magnification is changed, the imaging optical system satisfiesthe following conditions, instead of Conditions (1) and (2), in at leastone variable magnification state:

|En|/L>0.8  (1′)

|Ex|/|L/β|>0.8  (2′)

[0068] It is more favorable to satisfy the following conditions:

|En|/L>1.6  (1″)

|Ex|/|L/β|>1.6  (2″)

[0069] In the imaging optical system of the present invention, theF-number is defined by the following conditions:

1.0<MAXFNO<8.0  (3)

ΔFNO/Δβ|<5  (4)

[0070] where MAXFNO is the smallest object-side F-number where theimaging magnification of the imaging optical system is changed, ΔFNO isa difference between the object-side F-number at the minimummagnification and the object-side F-number at the maximum magnificationin the entire system of the imaging optical system, and Δβ is adifference between the minimum magnification and the maximummagnification in the entire system of the imaging optical system.

[0071] Also, the F-number refers to an amount expressing the brightnessof the optical system. As the value of the F-number becomes small, abrighter optical system is obtained.

[0072] If the F-number is extremely small, the number of lenses must beincreased in order to correct aberration. This causes the problem thatthe overall length of the optical system is increased. On the otherhand, an extremely large F-number is not suitable for motion picturephotography because of shortage in the amount of light.

[0073] However, when the optical system satisfies Condition (3), theF-number is neither extremely small nor large. The above problems thatthe overall length of the optical system is increased and the F-numberis not suitable for motion picture photography can thus be obviated.

[0074] If the value of |ΔFNO/Δβ| is extremely large, the fluctuation ofthe image-side F-number becomes remarkable in the magnification change.As a result, the brightness of the camera must be adjusted. However,when Condition (4) is satisfied, there is no need to adjust thebrightness of the camera.

[0075] It is desirable to satisfy the following conditions:

2.0<MAXFNO<5.6  (3′)

|ΔFNO/Δβ|<3  (4′)

[0076] It is more desirable to satisfy the following conditions:

3.0<MAXFNO<4.0  (3″)

|ΔFNO/Δβ|<1  (4″)

[0077] In the imaging optical system of the present invention, it isdesirable that the most object-side lens of the first lens unit has thepositive refractive power. When the most object-side lens of the firstlens unit is constructed as the positive lens, an off-axis beam of lightcan be lowered and thus aberration becomes small.

[0078] In the imaging optical system of the present invention, it isdesirable that the first lens unit includes, in order from the objectside, positive, negative, and positive lenses. When the first lens unitis constructed with the positive, negative, and positive lenses,chromatic aberration of magnification and off-axis chromatic aberrationcan be corrected.

[0079] In the imaging optical system of the present invention, it isdesirable to satisfy a condition described below. When this condition issatisfied, the fluctuation of off-axis aberration can be kept to aminimum.

0.6<|(R3f+R3b)/(R3f−R3b)|<5.0  (5)

[0080] where |(R3f+R3b)/(R3f−R3b) | is a virtual shape factor, R3f isthe radius of curvature of the most object-side surface of the thirdlens unit and R3b is the radius of curvature of the most image-sidesurface of the third lens unit.

[0081] Beyond the upper limit of the virtual shape factor, the radius ofcurvature of the most object-side surface of the third lens unitapproximates that of the most image-side surface of the third lens unit.As such, the refractive power of the third lens unit becomes extremelyweak. Consequently, when the imaging magnification is changed, theamount of movement of the third lens unit must be increased. When theamount of movement of the third lens unit is large, the ray height ofoff-axis light incident on the third lens unit fluctuates. Thus, thefluctuation of off-axis aberration becomes pronounced. Below the lowerlimit of the virtual shape factor, the refractive power of the thirdlens unit becomes extremely strong. As a result, the angle of incidenceof the off-axis beam on the third lens unit is increased, and thefluctuation of off-axis aberration caused by the movement of the thirdlens unit becomes heavy.

[0082] However, when Condition (5) is satisfied, the refractive power ofthe third lens unit is neither extremely high nor low, and the aboveproblem that the fluctuation of off-axis aberration is heavy can beobviated.

[0083] It is desirable to satisfy the following condition:

1.2<|(R3f+R3b)/(R3f−R3b)|<3.5  (5′)

[0084] It is more desirable to satisfy the following condition:

2.0<|(R3f+R3b)/(R3f−R3b)|<3.0  (5″)

[0085] In the imaging optical system of the present invention, it isdesirable that the third lens unit has at least two meniscus lenses,each with a convex surface directed toward the object side. It is moredesirable that the third lens unit has at least three meniscus lenses.More specifically, it is desirable that the third lens unit, forexample, has two negative meniscus lenses, each with a convex surfacedirected toward the object side, and one positive meniscus lens with aconvex surface directed toward the object side. Since the third lensunit is located close to the stop, off-axis rays are incident on thelenses of the third lens unit at almost the same angle, irrespective ofthe angle of view.

[0086] However, the meniscus lens in which a convex surface is directedtoward the object side, namely the object-side surface has the positiverefractive power, has nearly minimum deflection angles with respect toon- and off-axis light beams at individual angles of view, and hence theproduction of aberration can be prevented.

[0087] In accordance with the drawings, the embodiments of the presentinvention will be described below.

[0088] First Embodiment

[0089]FIGS. 1A, 1B, and 1C show optical arrangements, developed alongthe optical axis, at magnifications of 0.3×, 0.4×, and 0.5×,respectively, of the first embodiment of the imaging optical systemaccording to the present invention. FIGS. 2A, 2B, and 2C show aberrationcharacteristics in focusing at an imaging magnification of 0.4× of theimaging optical system in the first embodiment.

[0090] The imaging optical system of the first embodiment has a variablemagnification optical system Z. In FIG. 1A, reference symbol Prepresents a prism, CG represents a cover glass, and I represents animaging surface.

[0091] The variable magnification optical system Z comprises, in orderfrom the object side toward the image side, a first lens unit G1 withpositive refractive power, a second lens unit G2 with positiverefractive power, a third lens unit G3 with negative refractive power,an aperture stop S, and a fourth lens unit G4 with positive refractivepower.

[0092] The first lens unit G1 includes, in order from the object side, abiconvex lens L1 ₁, a biconcave lens L1 ₂, and a biconvex lens L1 ₃.

[0093] The second lens unit G2 includes, in order from the object side,a negative meniscus lens L2 ₁ with a convex surface directed toward theobject side, a biconvex lens L2 ₂, a negative meniscus lens L2 ₃ with aconcave surface directed toward the object side, and a biconvex lens L2₄.

[0094] The third lens unit G3 includes a positive meniscus lens L3 ₁with a convex surface directed toward the object side, a negativemeniscus lens L3 ₂ with a convex surface directed toward the objectside, and a negative meniscus lens L3 ₃ with a convex surface directedtoward the object side.

[0095] The fourth lens unit G4 includes a cemented doublet of abiconcave lens L4 ₁ and a biconvex lens L4 ₂, a biconcave lens L4 ₃, abiconvex lens L4 ₄, a biconvex lens L4 ₅, and a biconvex lens L4 ₆.

[0096] When the magnification is changed from 0.3× to 0.5× in focusingof an infinite object point, the first lens unit G1, after being movedonce toward the object side, is moved toward the image side, the secondlens unit G2 is moved toward the object side, the third lens unit G3 ismoved toward the image side together with the stop S, and the fourthlens unit G4 is moved toward the image side so that spacing between thethird and fourth lens units G3 and G4 is slightly widened. Also, theobject-to-image distance in the magnification change is kept constant.

[0097] Subsequently, numerical data of optical members constituting theimaging optical system of the first embodiment are shown below. In thenumerical data, r₀, r₁, r₂, . . . denote radii of curvature of surfacesof individual optical members shown in this order from the object side;d₀, d₁, d₂, . . . denote thicknesses (mm) of individual optical membersor air spacings between them; n_(e1), n_(e2), . . . denote refractiveindices of individual optical members at the e line; v_(e1), v_(e2), . .. denote Abbe's numbers of individual optical members at the e line.These symbols are also used for the numerical data of other embodimentsto be described later. Numerical data 1 Image height: 5.783 r₀ = ∞(object) d₀ = 50.000 r₁ = ∞ (object surface) d₁ = D1 r₂ = 189.5313 d₂ =7.308 n_(e2) = 1.48915 ν_(e2) = 70.04 r₃ = −117.0877 d₃ = 10.588 r₄ =−6124.8097 d₄ = 6.910 n_(e4) = 1.61639 ν_(e4) = 44.15 r₅ = 67.5133 d₅ =12.028 r₆ = 88.2299 d₆ = 8.685 n_(e6) = 1.43985 ν_(e6) = 94.53 r₇ =−425.3119 d₇ = D7 r₈ = 148.1127 d₈ = 6.000 n_(e8) = 1.61639 ν_(e8) =44.15 r₉ = 64.7754 d₉ = 5.355 r₁₀ = 88.2208 d₁₀ = 8.016 n_(e10) =1.43985 ν_(e10) = 94.53 r₁₁ = −81.9368 d₁₁ = 1.062 r₁₂ = −69.6148 d₁₂ =7.000 n_(e12) = 1.61639 ν_(e12) = 44.15 r₁₃ = −171.6506 d₁₃ = 17.627 r₁₄= 210.1703 d₁₄ = 6.814 n_(e14) = 1.43985 ν_(e14) = 94.53 r₁₅ = −82.3361d₁₅ = D15 r₁₆ = 40.6305 d₁₆ = 4.323 n_(e16) = 1.69417 ν_(e16) = 30.83r₁₇ = 250.0598 d₁₇ = 0.300 r₁₈ = 25.0517 d₁₈ = 9.360 n_(e18) = 1.72538ν_(e18) = 34.47 r₁₉ = 21.5375 d₁₉ = 1.156 r₂₀ = 41.2143 d₂₀ = 2.000n_(e20) = 1.72538 ν_(e20) = 34.47 r₂₁ = 15.8016 d₂₁ = 2.560 r₂₂ = ∞(aperture stop) d₂₂ = D22 r₂₃ = −29.2488 d₂₃ = 2.000 n_(e23) = 1.61669ν_(e23) = 44.02 r₂₄ = 23.4936 d₂₄ = 7.647 n_(e24) = 1.48915 ν_(e24) =70.04 r₂₅ = −17.8845 d₂₅ = 3.043 r₂₆ = −13.7038 d₂₆ = 1.417 n_(e26) =1.61639 ν_(e26) = 44.15 r₂₇ = 89.8893 d₂₇ = 4.829 r₂₈ = 707.1568 d₂₈ =8.564 n_(e28) = 1.43985 ν_(e28) = 94.53 r₂₉ = −18.1649 d₂₉ = 0.325 r₃₀ =69.4722 d₃₀ = 5.111 n_(e30) = 1.43985 ν_(e30) = 94.53 r₃₁ = −90.8646 d₃₁= 0.300 r₃₂ = 62.9985 d₃₂ = 4.778 n_(e32) = 1.43985 ν_(e32) = 94.53 r₃₃= −179.4454 d₃₃ = D33 r₃₄ = ∞ d₃₄ = 33.000 n_(e34) = 1.61173 ν_(e34) =46.30 r₃₅ = ∞ d₃₅ = 13.200 n_(e35) = 1.51825 ν_(e35) = 63.93 r₃₆ = ∞ d₃₆= 0.500 r₃₇ = ∞ (imaging surface) d₃₇ = 0.000 0.3× 0.4× 0.5× Zoom dataD1 39.880 37.812 44.358 D7 109.204 77.238 48.939 D15 3.000 37.903 60.723D22 3.552 4.754 6.263 D33 21.051 18.980 16.405 Parameters of conditionsMagnification: β Entrance pupil position: En 1160.856 20252.775−1133.552 Object-to-image distance: L 428.492 428.492 428.492 |En|/L2.709 47.265 2.645 Exit pupil position: Ex −352.468 −578.834 −1818.976|Ex|/|L/β| 0.247 0.540 2.123 F-number: FNO 3.500 3.536 3.598 FNOfluctuation: ΔFNO 0.098 |ΔFNO/Δβ| 0.490 Object-side radius of curvature:R3f 40.630 Image-side radius of curvature: R3b 15.802 |(R3f + R3b)/(R3f− R3b)| 2.273

[0098] Second Embodiment

[0099]FIGS. 3A, 3B, and 3C show optical arrangements, developed alongthe optical axis, at magnifications of 0.3×, 0.4×, and 0.5×,respectively, of the second embodiment of the imaging optical systemaccording to the present invention. FIGS. 4A, 4B, and 4C show aberrationcharacteristics in focusing at a magnification of 0.4× of the imagingoptical system in the second embodiment.

[0100] The imaging optical system of the second embodiment has thevariable magnification optical system Z.

[0101] The variable magnification optical system Z comprises, in orderfrom the object side toward the image side, the first lens unit G1 withpositive refractive power, the second lens unit G2 with positiverefractive power, the third lens unit G3 with negative refractive power,the aperture stop S, and the fourth lens unit G4 with positiverefractive power.

[0102] The first lens unit G1 includes, in order from the object side,the biconvex lens L1 ₁, a negative meniscus lens L1 ₂′ with a convexsurface directed toward the object side, and the biconvex lens L1 ₃.

[0103] The second lens unit G2, in order from the object side, thenegative meniscus lens L2 ₁ with a convex surface directed toward theobject side, the biconvex lens L2 ₂, the negative meniscus lens L2 ₃with a concave surface directed toward the object side, and the biconvexlens L2 ₄.

[0104] The third lens unit G3 includes the positive meniscus lens L3 ₁with a convex surface directed toward the object side, the negativemeniscus lens L3 ₂ with a convex surface directed toward the objectside, and the negative meniscus lens L3 ₃ with a convex surface directedtoward the object side.

[0105] The fourth lens unit G4 includes the cemented doublet of thebiconcave lens L4 ₁ and the biconvex lens L4 ₂, the biconcave lens L4 ₃,the biconvex lens L4 ₄, the biconvex lens L4 ₅, and the biconvex lens L4₆.

[0106] When the magnification is changed from 0.3× to 0.5× in focusingof the infinite object point, the first lens unit G1, after being movedonce toward the object side, is moved toward the image side, the secondlens unit G2 is moved toward the object side, the third lens unit G3remains fixed together with the stop S, and the fourth lens unit G4 ismoved toward the image side so that the spacing between the third andfourth lens units G3 and G4 is slightly widened. Also, theobject-to-image distance in the magnification change is kept constant.

[0107] Subsequently, numerical data of optical members constituting theimaging optical system of the second embodiment are shown below.Numerical data 2 Image height: 5.783 r₀ = ∞ (object) d₀ = 50.000 r₁ = ∞(object surface) d₁ = D1 r₂ = 172.4277 d₂ = 6.648 n_(e2) = 1.48915ν_(e2) = 70.04 r₃ = −112.2625 d₃ = 7.313 r₄ = 1492.6672 d₄ = 7.985n_(e4) = 1.61639 ν_(e4) = 44.15 r₅ = 62.4069 d₅ = 12.125 r₆ = 79.8565 d₆= 9.415 n_(e6) = 1.43985 ν_(e6) = 94.53 r₇ = −1585.7009 d₇ = D7 r₈ =151.8708 d₈ = 6.000 n_(e8) = 1.61639 ν_(e8) = 44.15 r₉ = 64.4718 d₉ =5.384 r₁₀ = 86.7203 d₁₀ = 8.163 n_(e10) = 1.43985 ν_(e10) = 94.53 r₁₁ =−80.8037 d₁₁ = 1.049 r₁₂ = −68.7719 d₁₂ = 6.410 n_(e12) = 1.61639ν_(e12) = 44.15 r₁₃ = −178.7270 d₁₃ = 16.603 r₁₄ = 219.0646 d₁₄ = 6.722n_(e14) = 1.43985 ν_(e14) = 94.53 r₁₅ = −81.1984 d₁₅ = D15 r₁₆ = 40.1465d₁₆ = 4.375 n_(e16) = 1.69417 ν_(e16) = 30.83 r₁₇ = 229.4681 d₁₇ = 0.300r₁₈ = 24.8118 d₁₈ = 9.366 n_(e18) = 1.72538 ν_(e18) = 34.47 r₁₉ =21.1952 d₁₉ = 1.169 r₂₀ = 40.9998 d₂₀ = 2.000 n_(e20) = 1.72538 ν_(e20)= 34.47 r₂₁ = 15.9793 d₂₁ = 2.555 r₂₂ = ∞ (aperture stop) d₂₂ = D22 r₂₃= −29.1565 d₂₃ = 2.000 n_(e23) = 1.61669 ν_(e23) = 44.02 r₂₄ = 23.6864d₂₄ = 7.373 n_(e24) = 1.48915 ν_(e24) = 70.04 r₂₅ = −18.0561 d₂₅ = 3.435r₂₆ = −13.7966 d₂₆ = 1.355 n_(e26) = 1.61639 ν_(e26) = 44.15 r₂₇ =84.7189 d₂₇ = 4.778 r₂₈ = 547.3608 d₂₈ = 8.544 n_(e28) = 1.43985 ν_(e28)= 94.53 r₂₉ = −18.0837 d₂₉ = 0.300 r₃₀ = 70.0296 d₃₀ = 5.063 n_(e30) =1.43985 ν_(e30) = 94.53 r₃₁ = −93.9274 d₃₁ = 0.388 r₃₂ = 58.3720 d₃₂ =4.869 n_(e32) = 1.43985 ν_(e32) = 94.53 r₃₃ = −203.9907 d₃₃ = D33 r₃₄ =∞ d₃₄ = 33.000 n_(e34) = 1.61173 ν_(e34) = 46.30 r₃₅ = ∞ d₃₅ = 13.200n_(e35) = 1.51825 ν_(e35) = 63.93 r₃₆ = ∞ d₃₆ = 0.500 r₃₇ = ∞ (imagingsurface) d₃₇ = 0.000 0.3× 0.4× 0.5× Zoom data D1 43.904 39.311 43.788 D7110.381 79.183 50.950 D15 3.089 38.880 62.637 D22 3.559 5.250 7.195 D3320.639 18.949 17.003 Parameters of conditions Magnification: β Entrancepupil position: En 1124.667 16516.516 −1141.823 Object-to-imagedistance: L 429.959 429.959 429.959 |En|/L 2.616 38.414 2.656 Exit pupilposition: Ex −351.154 −741.700 24496.963 |Ex|/|L/β| 0.245 0.690 28.488F-number: FNO 3.500 3.560 3.646 FNO fluctuation: ΔFNO 0.146 |ΔFNO/Δβ|0.729 Object-side radius of curvature: R3f 38.452 Image-side radius ofcurvature: R3b 17.589 |(R3f + R3b)/(R3f − R3b)| 2.686

[0108] Third Embodiment

[0109]FIGS. 5A, 5B, and 5C show optical arrangements, developed alongthe optical axis, at magnifications of 0.3×, 0.4×, and 0.5×,respectively, of the third embodiment of the imaging optical systemaccording to the present invention. FIGS. 6A, 6B, and 6C show aberrationcharacteristics in focusing at a magnification of 0.4× of the imagingoptical system in the third embodiment.

[0110] The imaging optical system of the third embodiment has thevariable magnification optical system Z.

[0111] The variable magnification optical system Z comprises, in orderfrom the object side toward the image side, the first lens unit G1 withpositive refractive power, the second lens unit G2 with positiverefractive power, the third lens unit G3 with negative refractive power,the aperture stop S, and the fourth lens unit G4 with positiverefractive power.

[0112] The first lens unit G1 includes, in order from the object side,the biconvex lens L1 ₁, the negative meniscus lens L1 ₂′ with a convexsurface directed toward the object side, and a positive meniscus lens L1₃′ with a convex surface directed toward the object side.

[0113] The second lens unit G2, in order from the object side, thenegative meniscus lens L2 ₁ with a convex surface directed toward theobject side, the biconvex lens L2 ₂, the negative meniscus lens L2 ₃with a concave surface directed toward the object side, and the biconvexlens L2 ₄.

[0114] The third lens unit G3 includes the positive meniscus lens L3 ₁with a convex surface directed toward the object side, the negativemeniscus lens L3 ₂ with a convex surface directed toward the objectside, and the negative meniscus lens L3 ₃ with a convex surface directedtoward the object side.

[0115] The fourth lens unit G4 includes the cemented doublet of thebiconcave lens L4 ₁ and the biconvex lens L4 ₂, the biconcave lens L4 ₃,the biconvex lens L4 ₄, the biconvex lens L4 ₅, and the biconvex lens L4₆.

[0116] When the magnification is changed from 0.3× to 0.5× in focusingof the infinite object point, the first lens unit G1, after being movedonce toward the object side, is moved toward the image side, the secondlens unit G2 is moved toward the object side, the third lens unit G3 ismoved toward the object side together with the stop S so that thespacing between the third and fourth lens units G3 and G4 is slightlywidened, and the fourth lens unit G4 remains fixed. Also, theobject-to-image distance in the magnification change is kept constant.

[0117] Subsequently, numerical data of optical members constituting theimaging optical system of the third embodiment are shown below.Numerical data 3 Image height: 5.783 r₀ = ∞ (object) d₀ = 50.000 r₁ = ∞(object surface) d₁ = D1 r₂ = 67.5689 d₂ = 7.816 n_(e2) = 1.48915 ν_(e2)= 70.04 r₃ = −335.3716 d₃ = 0.300 r₄ = 140.6380 d₄ = 6.025 n_(e4) =1.61639 ν_(e4) = 44.15 r₅ = 45.2535 d₅ = 8.810 r₆ = 57.6476 d₆ = 11.963n_(e6) = 1.43985 ν_(e6) = 94.53 r₇ = 109.0130 d₇ = D7 r₈ = 140.9050 d₈ =6.209 n_(e8) = 1.61639 ν_(e8) = 44.15 r₉ = 59.1517 d₉ = 5.421 r₁₀ =89.7738 d₁₀ = 7.460 n_(e10) = 1.43985 ν_(e10) = 94.53 r₁₁ = −74.4487 d₁₁= 1.335 r₁₂ = −57.6329 d₁₂ = 7.000 n_(e12) = 1.61639 ν_(e12) = 44.15 r₁₃= −145.4391 d₁₃ = 15.344 r₁₄ = 312.0611 d₁₄ = 8.089 n_(e14) = 1.43985ν_(e14) = 94.53 r₁₅ = −66.7614 d₁₅ = D15 r₁₆ = 42.2336 d₁₆ = 4.331n_(e16) = 1.69417 ν_(e16) = 30.83 r₁₇ = 254.0344 d₁₇ = 0.300 r₁₈ =24.1640 d₁₈ = 9.326 n_(e18) = 1.72538 ν_(e18) = 34.47 r₁₉ = 20.0169 d₁₉= 1.206 r₂₀ = 36.3821 d₂₀ = 2.000 n_(e20) = 1.72538 ν_(e20) = 34.47 r₂₁= 16.7574 d₂₁ = 2.601 r₂₂ = ∞ (aperture stop) d₂₂ = D22 r₂₃ = −26.7471d₂₃ = 2.030 n_(e23) = 1.61669 ν_(e23) = 44.02 r₂₄ = 24.0157 d₂₄ = 5.463n_(e24) = 1.48915 ν_(e24) = 70.04 r₂₅ = −17.6590 d₂₅ = 4.328 r₂₆ =−13.4729 d₂₆ = 1.058 n_(e26) = 1.61639 ν_(e26) = 44.15 r₂₇ = 93.0104 d₂₇= 4.726 r₂₈ = 913.0291 d₂₈ = 8.540 n_(e28) = 1.43985 ν_(e28) = 94.53 r₂₉= −17.8834 d₂₉ = 0.300 r₃₀ = 81.9603 d₃₀ = 6.985 n_(e30) = 1.43985ν_(e30) = 94.53 r₃₁ = −64.2115 d₃₁ = 3.523 r₃₂ = 60.0466 d₃₂ = 6.110n_(e32) = 1.43985 ν_(e32) = 94.53 r₃₃ = −318.5459 d₃₃ = 19.314 r₃₄ = ∞d₃₄ = 33.000 n_(e34) = 1.61173 ν_(e34) = 46.30 r₃₅ = ∞ d₃₅ = 13.200n_(e35) = 1.51825 ν_(e35) = 63.93 r₃₆ = ∞ d₃₆ = 0.500 r₃₇ = ∞ (imagingsurface) d₃₇ = 0.000 0.3× 0.4× 0.5× Zoom data D1 50.134 38.319 43.946 D7107.947 77.883 43.657 D15 3.000 42.757 69.242 D22 3.638 5.759 7.874Parameters of conditions Magnification: β Entrance pupil position: En1271.479 −18393.929 −1095.982 Object-to-image distance: L 429.334429.334 429.334 |En|/L 2.962 42.843 2.553 Exit pupil position: Ex−362.746 −906.100 4824.866 |Ex|/|L/β| 0.253 0.844 5.619 F-number: FNO3.500 3.593 3.687 FNO fluctuation: ΔFNO 0.187 |ΔFNO/Δβ| 0.935Object-side radius of curvature: 42.234 R3f Image-side radius ofcurvature: 16.757 R3b |(R3f + R3b)/(R3f − R3b)| 2.316

[0118] Fourth Embodiment

[0119]FIGS. 7A, 7B, and 7C show optical arrangements, developed alongthe optical axis, at magnifications of 0.3×, 0.4×, and 0.5×,respectively, of the fourth embodiment of the imaging optical systemaccording to the present invention. FIGS. 8A, 8B, and 8C show aberrationcharacteristics in focusing at a magnification of 0.4× of the imagingoptical system in the fourth embodiment.

[0120] The imaging optical system of the fourth embodiment has thevariable magnification optical system Z.

[0121] The variable magnification optical system Z comprises, in orderfrom the object side toward the image side, the first lens unit G1 withpositive refractive power, the second lens unit G2 with positiverefractive power, the third lens unit G3 with negative refractive power,the aperture stop S, and the fourth lens unit G4 with positiverefractive power.

[0122] The first lens unit G1 includes, in order from the object side,the biconvex lens L1 ₁, the negative meniscus lens L1 ₂′ with a convexsurface directed toward the object side, and the positive meniscus lensL1 ₃′ with a convex surface directed toward the object side.

[0123] The second lens unit G2, in order from the object side, thenegative meniscus lens L2 ₁ with a convex surface directed toward theobject side, the biconvex lens L2 ₂, the negative meniscus lens L2 ₃with a concave surface directed toward the object side, and the biconvexlens L2 ₄.

[0124] The third lens unit G3 includes the positive meniscus lens L3 ₁with a convex surface directed toward the object side, the negativemeniscus lens L3 ₂ with a convex surface directed toward the objectside, and the negative meniscus lens L3 ₃ with a convex surface directedtoward the object side.

[0125] The fourth lens unit G4 includes the cemented doublet of thebiconcave lens L4 ₁ and the biconvex lens L4 ₂, the biconcave lens L4 ₃,the biconvex lens L4 ₄, the biconvex lens L4 ₅, and the biconvex lens L4₆.

[0126] When the magnification is changed from 0.3× to 0.5× in focusingof the infinite object point, the first lens unit G1 is moved toward theimage side, the second lens unit G2 is moved toward the object side, thethird lens unit G3 is moved toward the image side, and the fourth lensunit G4 is moved toward the image side together with the stop S so thatthe spacing between the third and fourth lens units G3 and G4 isslightly widened. Also, the object-to-image distance in themagnification change is kept constant.

[0127] Subsequently, numerical data of optical members constituting theimaging optical system of the fourth embodiment are shown below.Numerical data 4 Image height: 5.783 r₀ = ∞ (object) d₀ = 50.000 r₁ = ∞(object surface) d₁ = D1 r₂ = 107.8560 d₂ = 7.337 n_(e2) = 1.48915ν_(e2) = 70.04 r₃ = −119.7849 d₃ = 3.971 r₄ = 454.1088 d₄ = 7.857 n_(e4)= 1.61639 ν_(e4) = 44.15 r₅ = 49.9355 d₅ = 12.309 r₆ = 64.2291 d₆ =6.018 n_(e6) = 143985 ν_(e6) = 94.53 r₇ = 300.8668 d₇ = D7 r₈ = 126.3256d₈ = 6.000 n_(e8) = 1.61639 ν_(e8) = 44.15 r₉ = 56.4062 d₉ = 6.775 r₁₀ =81.4055 d₁₀ = 8.793 n_(e10) = 1.43985 ν_(e10) = 94.53 r₁₁ = −83.1434 d₁₁= 1.494 r₁₂ = −63.8486 d₁₂ = 7.000 n_(e12) = 1.61639 ν_(e12) = 44.15 r₁₃= −133.7944 d₁₃ = 15.757 r₁₄ = 330.3809 d₁₄ = 7.640 n_(e14) = 1.43985ν_(e14) = 94.53 r₁₅ = −69.3107 d₁₅ = D15 r₁₆ = 40.1299 d₁₆ = 4.652n_(e16) = 1.69417 ν_(e16) = 30.83 r₁₇ = 187.3566 d₁₇ = 0.300 r₁₈ =24.6796 d₁₈ = 9.359 n_(e18) = 1.72538 ν_(e18) = 34.47 r₁₉ = 20.3802 d₁₉= 1.377 r₂₀ = 39.2697 d₂₀ = 2.000 n_(e20) = 1.72538 ν_(e20) = 34.47 r₂₁= 16.0804 d₂₁ = D21 r₂₂ = ∞ (aperture stop) d₂₂ = 3.575 r₂₃ = −30.0984d₂₃ = 2.000 n_(e23) = 1.61669 ν_(e23) = 44.02 r₂₄ = 23.9795 d₂₄ = 8.757n_(e24) = 1.48915 ν_(e24) = 70.04 r₂₅ = −18.9682 d₂₅ = 3.837 r₂₆ =−14.1963 d₂₆ = 0.817 n_(e26) = 1.61639 ν_(e26) = 44.15 r₂₇ = 101.4717d₂₇ = 4.565 r₂₈ = 1012.5847 d₂₈ = 8.419 n_(e28) = 1.43985 ν_(e28) =94.53 r₂₉ = −18.1103 d₂₉ = 0.629 r₃₀ = 69.9749 d₃₀ = 4.880 n_(e30) =1.43985 ν_(e30) = 94.53 r₃₁ = −123.8898 d₃₁ = 0.928 r₃₂ = 61.1846 d₃₂ =4.997 n_(e32) = 1.43985 ν_(e32) = 94.53 r₃₃ = −136.6736 d₃₃ = D33 r₃₄ =∞ d₃₄ = 33.000 n_(e34) = 1.61173 ν_(e34) = 46.30 r₃₅ = ∞ d₃₅ = 13.200n_(e35) = 1.51825 ν_(e35) = 63.93 r₃₆ =∞ d₃₆ = 0.500 r₃₇ = ∞ (imagingsurface) d₃₇ = 0.000 0.3× 0.4× 0.5× Zoom data D1 38.765 44.451 53.283 D7117.344 81.410 52.958 D15 3.000 34.932 56.369 D21 2.614 3.787 5.228 D3321.660 18.803 15.544 Parameters of conditions Magnification: β Entrancepupil position: En 1117.828 5171.585 −1158.986 Object-to-image distance:L 432.125 432.125 432.125 |En|/L 2.587 11.968 2.682 Exit pupil position:Ex −357.630 −357.630 −357.630 |Ex|/|L/β| 0.248 0.331 0.485 F-number: FNO3.500 3.479 3.414 FNO fluctuation: ΔFNO −0.046 |ΔFNO/Δβ| −0.228Object-side radius of curvature: R3f 40.130 Image-side radius ofcurvature: R3b 16.080 |(R3f + R3b)/(R3f − R3b)| 2.337

[0128] Fifth Embodiment

[0129]FIGS. 9A, 9B, and 9C show optical arrangements, developed alongthe optical axis, at magnifications of 0.3×, 0.4×, and 0.5×,respectively, of the fifth embodiment of the imaging optical systemaccording to the present invention. FIGS. 10A, 10B, and 10C showaberration characteristics in focusing at a magnification of 0.4× of theimaging optical system in the fifth embodiment.

[0130] The imaging optical system of the fifth embodiment has thevariable magnification optical system Z.

[0131] The variable magnification optical system Z comprises, in orderfrom the object side toward the image side, the first lens unit G1 withpositive refractive power, the second lens unit G2 with positiverefractive power, the third lens unit G3 with negative refractive power,the aperture stop S, and the fourth lens unit G4 with positiverefractive power.

[0132] The first lens unit G1 includes, in order from the object side, aplano-convex lens L1 ₁′ with a convex surface directed toward the objectside and a plane surface directed toward the image side, the negativemeniscus lens L1 ₂′ with a convex surface directed toward the objectside, and the positive meniscus lens L1 ₃′ with a convex surfacedirected toward the object side.

[0133] The second lens unit G2, in order from the object side, thenegative meniscus lens L2, with a convex surface directed toward theobject side, the biconvex lens L2 ₂, the negative meniscus lens L2 ₃with a concave surface directed toward the object side, and the biconvexlens L2 ₄.

[0134] The third lens unit G3 includes the positive meniscus lens L3 ₁with a convex surface directed toward the object side, the negativemeniscus lens L3 ₂ with a convex surface directed toward the objectside, and the negative meniscus lens L3 ₃ with a convex surface directedtoward the object side.

[0135] The fourth lens unit G4 includes the cemented doublet of thebiconcave lens L4 ₁ and the biconvex lens L4 ₂, the biconcave lens L4 ₃,the biconvex lens L4 ₄, the biconvex lens L4 ₅, and the biconvex lens L4₆.

[0136] When the magnification is changed from 0.3× to 0.5× in focusingof the infinite object point, the first lens unit G1, after being movedonce toward the object side, is moved toward the image side, the secondlens unit G2 is moved toward the object side, the third lens unit G3 ismoved toward the object side so that the spacing between the third andfourth lens units G3 and G4 is slightly widened, and the fourth lensunit G4 remains fixed together with the stop S. Also, theobject-to-image distance in the magnification change is kept constant.

[0137] Subsequently, numerical data of optical members constituting theimaging optical system of the fifth embodiment are shown below.Numerical data 5 Image height: 5.783 r₀ = ∞ (object) d₀ = 50.000 r₁ = ∞(object surface) d₁ = D1 r₂ = 53.6678 d₂ = 7.850 n_(e2) = 1.48915 ν_(e2)= 70.04 r₃ = ∞ d₃ = 0.300 r₄ = 74.4381 d₄ = 6.000 n_(e4) = 1.61639ν_(e4) = 44.15 r₅ = 34.5362 d₅ = 8.043 r₆ = 39.1043 d₆ = 4.857 n_(e6) =1.43985 ν_(e6) = 94.53 r₇ = 52.1576 d₇ = D7 r₈ = 149.0540 d₈ = 6.000n_(e8) = 1.61639 ν_(e8) = 44.15 r₉ = 50.6084 d₉ = 6.908 r₁₀ = 78.4447d₁₀ = 9.096 n_(e10) = 1.43985 ν_(e10) = 94.53 r₁₁ = −67.1214 d₁₁ = 1.239r₁₂ = −55.5198 d₁₂ = 7.000 n_(e12) = 1.61639 ν_(e12) = 44.15 r₁₃ =−130.4767 d₁₃ = 17.549 r₁₄ = 526.4312 d₁₄ = 10.495 n_(e14) = 1.43985ν_(e14) = 94.53 r₁₅ = −60.7655 d₁₅ = D15 r₁₆ = 42.8799 d₁₆ = 4.607n_(e16) = 1.69417 ν_(e16) = 30.83 r₁₇ = 241.5957 d₁₇ = 0.300 r₁₈ =24.0062 d₁₈ = 9.266 n_(e18) = 1.72538 ν_(e18) = 34.47 r₁₉ = 20.0630 d₁₉= 1.423 r₂₀ = 37.0493 d₂₀ = 2.000 n_(e20) = 1.72538 ν_(e20) = 34.47 r₂₁= 16.8163 d₂₁ = D21 r₂₂ = ∞ (aperture stop) d₂₂ = 3.685 r₂₃ = −27.7248d₂₃ = 2.000 n_(e23) = 1.61669 ν_(e23) = 44.02 r₂₄ = 25.1231 d₂₄ = 5.991n_(e24) = 1.48915 ν_(e24) = 70.04 r₂₅ = −18.8837 d₂₅ = 4.943 r₂₆ =−14.1386 d₂₆ = 0.553 n_(e26) = 1.61639 ν_(e26) = 44.15 r₂₇ = 103.4372d₂₇ = 4.610 r₂₈ = 946.2142 d₂₈ = 8.426 n_(e28) = 1.43985 ν_(e28) = 94.53r₂₉ = −18.1453 d₂₉ = 0.300 r₃₀ = 79.1515 d₃₀ = 7.210 n_(e30) = 1.43985ν_(e30) = 94.53 r₃₁ = −65.2376 d₃₁ = 5.640 r₃₂ = 63.0290 d₃₂ = 6.581n_(e32) = 1.43985 ν_(e32) = 94.53 r₃₃ = −291.4522 d₃₃ = 19.405 r₃₄ = ∞d₃₄ = 33.000 n_(e34) = 1.61173 ν_(e34) = 46.30 r₃₅ = ∞ d₃₅ = 13.200n_(e35) = 1.51825 ν_(e35) = 63.93 r₃₆ = ∞ d₃₆ = 0.500 r₃₇ = ∞ (imagingsurface) d₃₇ = 0.000 0.3× 0.4× 0.5× Zoom data D1 42.960 38.372 47.817 D7105.480 70.527 33.769 D15 3.000 40.551 66.211 D21 2.679 4.670 6.322Parameters of conditions Magnification: β Entrance pupil position: En1295.110 24846.034 −1103.070 Object-to-image distance: L 423.096 423.096423.096 |En|/ L 3.061 58.724 2.607 Exit pupil position: Ex −366.274−366.274 −366.274 |Ex|/|L/β| 0.260 0.346 0.433 F-number: FNO 3.500 3.5003.500 FNO fluctuation : ΔFNO 0.000 |ΔFNO/Δβ| −0.002 Object-side radiusof curvature: R3f 42.880 Image-side radius of curvature: R3b 16.816|(R3f + R3b)/(R3f − R3b)| 2.290

[0138] Sixth Embodiment

[0139]FIGS. 11A, 11B, and 11C show optical arrangements, developed alongthe optical axis, at magnifications of 0.3×, 0.4×, and 0.5×,respectively, of the sixth embodiment of the imaging optical systemaccording to the present invention. FIGS. 12A, 12B, and 12C showaberration characteristics in focusing at a magnification of 0.4× of theimaging optical system in the sixth embodiment.

[0140] The imaging optical system of the sixth embodiment has thevariable magnification optical system Z.

[0141] The variable magnification optical system Z comprises, in orderfrom the object side toward the image side, the first lens unit G1 withpositive refractive power, the second lens unit G2 with positiverefractive power, the third lens unit G3 with negative refractive power,the aperture stop S, and the fourth lens unit G4 with positiverefractive power.

[0142] The first lens unit G1 includes, in order from the object side,the biconvex lens L1 ₁, the biconcave lens L1 ₂, and the biconvex lensL1 ₃.

[0143] The second lens unit G2, in order from the object side, thenegative meniscus lens L2 ₁ with a convex surface directed toward theobject side, the biconvex lens L2 ₂, the negative meniscus lens L2 ₃with a concave surface directed toward the object side, and a positivemeniscus lens L2 ₄′ with a concave surface directed toward the objectside.

[0144] The third lens unit G3 includes the positive meniscus lens L3 ₁with a convex surface directed toward the object side, the negativemeniscus lens L3 ₂ with a convex surface directed toward the objectside, and the negative meniscus lens L3 ₃ with a convex surface directedtoward the object side.

[0145] The fourth lens unit G4 includes the cemented doublet of thebiconcave lens L4 ₁ and the biconvex lens L4 ₂, the biconcave lens L4 ₃,the biconvex lens L4 ₄, the biconvex lens L4 ₅, and the biconvex lens L4₆.

[0146] When the magnification is changed from 0.3× to 0.5× in focusingof the infinite object point, the first lens unit G1 is moved toward theobject side, the second lens unit G2 is moved toward the object side sothat spacing between the first and second lens units G1 and G2 iswidened, the third lens unit G3 is moved together with the stop S towardthe image side, and the fourth lens unit G4 is moved toward the imageside so that the spacing between the third and fourth lens units G3 andG4 is slightly widened. Also, the object-to-image distance in themagnification change is kept constant.

[0147] Subsequently, numerical data of optical members constituting theimaging optical system of the sixth embodiment are shown below.Numerical data 6 Image height: 5.783 r₀ = ∞ (object) d₀ = 50.000 r₁ = ∞(object surface) d₁ = D1 r₂ = 361.3250 d₂ = 12.000 n_(e2) = 1.48915ν_(e2) = 70.04 r₃ = −65.3190 d₃ = 0.300 r₄ = −90.3503 d₄ = 8.000 n_(e4)= 1.61639 ν_(e4) = 44.15 r₅ = 45.5593 d₅ = 11.355 r₆ = 65.7955 d₆ =12.000 n_(e6) = 1.43985 ν_(e6) = 94.53 r₇ = −101.4028 d₇ = D7 r₈ =113.0032 d₈ = 7.000 n_(e8) = 1.61639 ν_(e8) = 44.15 r₉ = 53.1618 d₉ =7.854 r₁₀ = 84.6315 d₁₀ = 8.348 n_(e10) = 1.43985 ν_(e10) = 94.53 r₁₁ =−82.9242 d₁₁ = 2.346 r₁₂ = −51.6817 d₁₂ = 6.901 n_(e12) = 1.61639ν_(e12) = 44.15 r₁₃ = −78.9538 d₁₃ = 0.300 r₁₄ = −746.1406 d₁₄ = 7.363n_(e14) = 1.43985 ν_(e14) = 94.53 r₁₅ = −54.9986 d₁₅ = D15 r₁₆ = 40.2152d₁₆ = 4.672 n_(e16) = 1.69417 ν_(e16) = 30.83 r₁₇ = 202.9669 d₁₇ = 0.300r₁₈ = 25.2156 d₁₈ = 9.337 n_(e18) = 1.72538 ν_(e18) = 34.47 r₁₉ =20.5989 d₁₉ = 1.486 r₂₀ = 47.2290 d₂₀ = 2.000 n_(e20) = 1.72538 ν_(e20)= 34.47 r₂₁ = 17.1952 d₂₁ = D21 r₂₂ = ∞ (aperture stop) d₂₂ = 8.090 r₂₃= −31.8155 d₂₃ = 12.000 n_(e23) = 1.61669 ν_(e23) = 44.02 r₂₄ = 23.4115d₂₄ = 6.316 n_(e24) = 1.48915 ν_(e24) = 70.04 r₂₅ = −23.1015 d₂₅ = 1.525r₂₆ = −17.3296 d₂₆ = 0.137 n_(e26) = 1.61639 ν_(e26) = 44.15 r₂₇ =121.5936 d₂₇ = 4.365 r₂₈ = 236.9154 d₂₈ = 8.477 n_(e28) = 1.43985ν_(e28) = 94.53 r₂₉ = −20.8758 d₂₉ = 0.300 r₃₀ = 78.3373 d₃₀ = 5.274n_(e30) = 1.43985 ν_(e30) = 94.53 r₃₁ = −103.6059 d₃₁ = 0.983 r₃₂ =81.5041 d₃₂ = 5.879 n_(e32) = 1.43985 ν_(e32) = 94.53 r₃₃ = −103.9512d₃₃ = D33 r₃₄ = ∞ d₃₄ = 33.000 n_(e34) = 1.61173 ν_(e34) = 46.30 r₃₅ = ∞d₃₅ = 13.200 n_(e35) = 1.51825 ν_(e35) = 63.93 r₃₆ = ∞ d₃₆ = 0.500 r₃₇ =∞ (imaging surface) d₃₇ = 0.000 0.3× 0.4× 0.5× Zoom data D1 68.66851.352 36.703 D7 65.281 56.350 50.311 D15 3.000 32.024 53.396 D21 2.7702.825 3.398 D33 20.686 17.854 16.597 Parameters of conditionsMagnification: β Entrance pupil position: En 140.733 198.229 329.610Object-to-image distance: L 412.012 412.012 412.012 |En|/L 0.342 0.4810.800 Exit pupil position: Ex 2022.944 2022.944 2022.944 |Ex|/|L/β|1.473 1.964 2.455 F-number: FNO 3.500 3.511 3.516 FNO fluctuation: ΔFNO0.016 |ΔFNO/Δβ| 0.082 Object-side radius of curvature: R3f 40.215Image-side radius of curvature: R3b 17.195 |(R3f + R3b)/(R3f − R3b)|2.494

[0148] Seventh Embodiment

[0149]FIGS. 13A, 13B, and 13C show optical arrangements, developed alongthe optical axis, at magnifications of 0.3×, 0.4×, and 0.5×,respectively, of the seventh embodiment of the imaging optical systemaccording to the present invention. FIGS. 14A, 14B, and 14C showaberration characteristics in focusing at a magnification of 0.4× of theimaging optical system in the seventh embodiment.

[0150] The imaging optical system of the seventh embodiment has thevariable magnification optical system Z. In FIG. 13A, reference symbolGL designates a plane-parallel plate and P1 and P2 designate prisms.

[0151] The variable magnification optical system Z comprises, in orderfrom the object side toward the image side, the first lens unit G1 withpositive refractive power, the second lens unit G2 with positiverefractive power, the third lens unit G3 with negative refractive power,the aperture stop S, and the fourth lens unit G4 with positiverefractive power.

[0152] The first lens unit G1 includes, in order from the object side,the biconvex lens L1 ₁, the negative meniscus lens L1 ₂′ with a convexsurface directed toward the object side, and the positive meniscus lensL1 ₃′ with a convex surface directed toward the object side.

[0153] The second lens unit G2, in order from the object side, thenegative meniscus lens L2 ₁ with a convex surface directed toward theobject side, the biconvex lens L2 ₂, the negative meniscus lens L2 ₃with a concave surface directed toward the object side, and the biconvexlens L2 ₄.

[0154] The third lens unit G3 includes the positive meniscus lens L3 ₁with a convex surface directed toward the object side, the negativemeniscus lens L3 ₂ with a convex surface directed toward the objectside, and the negative meniscus lens L3 ₃ with a convex surface directedtoward the object side.

[0155] The fourth lens unit G4 includes the cemented doublet of thebiconcave lens L4 ₁ and the biconvex lens L4 ₂, the biconcave lens L4 ₃,a positive meniscus lens L4 ₄′ with a concave surface directed towardthe object side, the biconvex lens L4 ₅, and the biconvex lens L4 ₆.

[0156] When the magnification is changed from 0.3× to 0.5× in focusingof the infinite object point, the first lens unit G1 is moved toward theobject side, the second lens unit G2 is moved toward the object side sothat the spacing between the first and second lens units G1 and G2 isnarrowed, the third lens unit G3 is moved together with the stop Stoward the image side, and the fourth lens unit G4 is moved toward theimage side so that the spacing between the third and fourth lens unitsG3 and G4 is slightly widened. Also, the object-to-image distance in themagnification change is kept constant.

[0157] Subsequently, numerical data of optical members constituting theimaging optical system of the seventh embodiment are shown below.Numerical data 7 Image height: 5.783 r₀ = ∞ (object) d₀ = 51.000 r₁ = ∞(object surface) d₁ = 9.260 n_(e1) = 1.51825 ν_(e1) = 63.93 r₂ = ∞ d₂ =2.740 r₃ = ∞ d₃ = 35.000 r₄ = ∞ d₄ = 60.000 n_(e4) = 1.51825 ν_(e4) =63.93 r₅ = ∞ d₅ = D5 r₆ = 206.3131 d₆ = 6.508 n_(e6) = 1.48915 ν_(e6) =70.04 r₇ = −156.0897 d₇ = 15.114 r₈ = 130.1657 d₈ = 8.000 n_(e8) =1.61639 ν_(e8) = 44.15 r₉ = 61.3830 d₉ = 1.693 r₁₀ = 80.8720 d₁₀ =12.000 n_(e10) = 1.43985 ν_(e10) = 94.53 r₁₁ = 232.8980 d₁₁ = D11 r₁₂ =672.7620 d₁₂ = 6.836 n_(e12) = 1.61639 ν_(e12) = 44.15 r₁₃ = 82.8549 d₁₃= 2.818 r₁₄ = 110.5678 d₁₄ = 9.282 n_(e14) = 1.43985 ν_(e14) = 94.53 r₁₅= −65.4332 d₁₅ = 0.300 r₁₆ = −67.0268 d₁₆ = 6.107 n_(e16) = 1.61639ν_(e16) = 44.15 r₁₇ = −156.9702 d₁₇ = 50.171 r₁₈ = 160.2358 d₁₈ = 10.874n_(e18) = 1.43985 ν_(e18) = 94.53 r₁₉ = −98.7058 d₁₉ = D19 r₂₀ = 37.4259d₂₀ = 5.034 n_(e20) = 1.69417 ν_(e20) = 30.83 r₂₁ = 212.9113 d₂₁ = 0.300r₂₂ = 22.9775 d₂₂ = 8.363 n_(e22) = 1.72538 ν_(e22) = 34.47 r₂₃ =18.2286 d₂₃ = 1.827 r₂₄ = 101.2051 d₂₄ = 2.247 n_(e24) = 1.72538 ν_(e24)= 34.47 r₂₅ = 17.6992 d₂₅ = 2.554 r₂₆ = ∞ (aperture stop) d₂₆ = D26 r₂₇= −55.3149 d₂₇ = 2.589 n_(e27) = 1.61669 ν_(e27) = 44.02 r₂₈ = 20.3875d₂₈ = 11.136 n_(e28) = 1.48915 ν_(e28) = 70.04 r₂₉ = −22.7793 d₂₉ =2.967 r₃₀ = −17.4070 d₃₀ = 2.255 n_(e30) = 1.61639 ν_(e30) = 44.15 r₃₁ =660.0000 d₃₁ = 5.164 r₃₂ = −361.4116 d₃₂ = 9.280 n_(e32) = 1.43985ν_(e32) = 94.53 r₃₃ = −21.6618 d₃₃ = 0.300 r₃₄ = 57.4166 d₃₄ = 5.104n_(e34) = 1.43985 ν_(e34) = 94.53 r₃₅ = −177.5066 d₃₅ = 0.350 r₃₆ =61.7155 d₃₆ = 4.849 n_(e36) = 1.43985 ν_(e36) = 94.53 r₃₇ = −672.7620d₃₇ = D37 r₃₈ = ∞ d₃₈ = 33.000 n_(e38) = 1.61173 ν_(e38) = 46.30 r₃₉ = ∞d₃₉ = 13.200 n_(e39) = 1.51825 ν_(e39) = 63.93 r₄₀ = ∞ d₄₀ = 0.500 r₄₁ =∞ (imaging surface) d₄₁ = 0.000 0.3× 0.4× 0.5× Zoom data D5 32.14228.009 24.962 D11 58.194 27.683 8.473 D19 3.000 39.963 64.634 D26 3.3405.440 7.048 D37 23.777 19.357 15.336 Parameters of conditionsMagnification: β Entrance pupil position: En 1215.330 17052.978−1195.682 Object-to-image distance: L 467.675 467.675 467.675 |En|/L2.599 36.463 2.557 Exit pupil position: Ex −361.027 −890.944 −13016.681|Ex|/|L/β| 0.232 0.762 13.916 F-number: FNO 3.500 3.517 3.556 FNOfluctuation: ΔFNO 0.056 |ΔFNO/Δβ| 0.280 Object-side radius of curvature:37.426 R3f Image-side radius of curvature: 17.699 R3b |(R3f + R3b)/(R3f− R3b)| 2.794

[0158] Eighth Embodiment

[0159]FIGS. 15A, 15B, and 15C show optical arrangements, developed alongthe optical axis, at magnifications of 0.3×, 0.4×, and 0.5×,respectively, of the eighth embodiment of the imaging optical systemaccording to the present invention. FIGS. 16A, 16B, and 16C showaberration characteristics in focusing at a magnification of 0.4× of theimaging optical system in the eighth embodiment.

[0160] The imaging optical system of the eighth embodiment has thevariable magnification optical system Z.

[0161] The variable magnification optical system Z comprises, in orderfrom the object side toward the image side, the first lens unit G1 withpositive refractive power, the second lens unit G2 with positiverefractive power, the third lens unit G3 with negative refractive power,the aperture stop S, and the fourth lens unit G4 with positiverefractive power.

[0162] The first lens unit G1 includes, in order from the object side, apositive meniscus lens L1 ₁″ with a concave surface directed toward theobject side, the negative meniscus lens L1 ₂′ with a concave surfacedirected toward the object side, and the biconvex lens L1 ₃.

[0163] The second lens unit G2, in order from the object side, thenegative meniscus lens L2 ₁ with a convex surface directed toward theobject side, the biconvex lens L2 ₂, the negative meniscus lens L2 ₃with a concave surface directed toward the object side, the positivemeniscus lens L2 ₄′ with a concave surface directed toward the objectside, and a positive meniscus lens L2 ₅ with a convex surface directedtoward the object side.

[0164] The third lens unit G3 includes a biconvex lens L3 ₁′, thenegative meniscus lens L3 ₂ with a convex surface directed toward theobject side, and the negative meniscus lens L3 ₃ with a convex surfacedirected toward the object side.

[0165] The fourth lens unit G4 includes a negative meniscus lens L4 ₁′with a convex surface directed toward the object side, a positivemeniscus lens L4 ₂′ with a concave surface directed toward the objectside, a negative meniscus lens L4 ₃′ with a concave surface directedtoward the object side, the positive meniscus lens L4 ₄′ with a concavesurface directed toward the object side, the biconvex lens L4 ₅, and apositive meniscus lens L4 ₆, with a convex surface directed toward theobject side.

[0166] When the magnification is changed from 0.3× to 0.5× in focusingof the infinite object point, the first lens unit G1 is moved toward theobject side, the second lens unit G2 is moved toward the object side sothat the spacing between the first and second lens units G1 and G2 iswidened, the third lens unit G3 is moved together with the stop S towardthe object side so that the spacing between the second and third lensunits G2 and G3 is slightly widened, and the fourth lens unit G4, afterbeing slightly moved once toward the image side, is slightly movedtoward the object side. Also, the object-to-image distance in themagnification change is kept constant.

[0167] Subsequently, numerical data of optical members constituting theimaging optical system of the eighth embodiment are shown below.Numerical data 8 Image height: 5.783 r₀ = ∞ (object) d₀ = 51.000 r₁ = ∞(object surface) d₁ = 9.260 n_(e1) = 1.51825 ν_(e1) = 63.93 r₂ = ∞ d₂ =2.740 r₃ = ∞ d₃ = 35.000 r₄ = ∞ d₄ = 60.000 n_(e4) = 1.51825 ν_(e4) =63.93 r₅ = ∞ d₅ = D5 r₆ = −218.393 d₆ = 11.966 n_(e6) = 1.48915 ν_(e6) =70.04 r₇ = −59.981 d₇ = 0.724 r₈ = −58.074 d₈ = 8.000 n_(e8) = 1.61639ν_(e8) = 44.15 r₉ = −192.015 d₉ = 0.300 r₁₀ = 453.258 d₁₀ = 11.399n_(e10) = 1.43985 ν_(e10) = 94.53 r₁₁ = −95.008 d₁₁ = D11 r₁₂ = 111.240d₁₂ = 6.982 n_(e12) = 1.61639 ν_(e12) = 44.15 r₁₃ = 49.021 d₁₃ = 0.808r₁₄ = 52.125 d₁₄ = 6.307 n_(e14) = 1.43985 ν_(e14) = 94.53 r₁₅ =−602.409 d₁₅ = 3.345 r₁₆ = −51.702 d₁₆ = 7.000 n_(e16) = 1.61639 ν_(e16)= 44.15 r₁₇ = −123.131 d₁₇ = 0.300 r₁₈ = −267.367 d₁₈ = 5.244 n_(e18) =1.43985 ν_(e18) = 94.53 r₁₉ = −59.230 d₁₉ = 0.300 r₂₀ = 62.890 d₂₀ =5.562 n_(e20) = 1.43985 ν_(e20) = 94.53 r₂₁ = 208.855 d₂₁ = D21 r₂₂ =109.670 d₂₂ = 4.560 n_(e22) = 1.67765 ν_(e22) = 31.84 r₂₃ = −261.555 d₂₃= 4.236 r₂₄ = 27.656 d₂₄ = 9.660 n_(e24) = 1.83945 ν_(e24) = 42.47 r₂₅ =22.416 d₂₅ = 3.719 r₂₆ = 591.785 d₂₆ = 2.000 n_(e26) = 1.83945 ν_(e26) =42.47 r₂₇ = 32.027 d₂₇ = 2.504 r₂₈ = ∞ (aperture stop) d₂₈ = D28 r₂₉ =235.972 d₂₉ = 3.058 n_(e29) = 1.61639 ν_(e29) = 44.15 r₃₀ = 39.062 d₃₀ =3.236 r₃₁ = −23.495 d₃₁ = 6.117 n_(e31) = 1.43985 ν_(e31) = 94.53 r₃₂ =−17.821 d₃₂ = 0.300 r₃₃ = −18.080 d₃₃ = 4.802 n_(e33)= 1.61639 ν_(e33) =44.15 r₃₄ = −31.126 d₃₄ = 0.300 r₃₅ = −67.557 d₃₅ = 4.329 n_(e35) =1.43985 ν_(e35) = 94.53 r₃₆ = −32.513 d₃₆ = 0.300 r₃₇ = 81.623 d₃₇ =4.159 n_(e37) = 1.43985 ν_(e37) = 94.53 r₃₈ = −357.038 d₃₈ = 0.484 r₃₉ =34.763 d₃₉ = 5.000 n_(e39) = 1.43985 ν_(e39) = 94.53 r₄₀ = 244.020 d₄₀ =D40 r₄₁ = ∞ d₄₁ = 33.000 n_(e41) = 1.61173 ν_(e41) = 46.30 r₄₂ = ∞ d₄₂ =13.200 n_(e42) = 1.51825 ν_(e42) = 63.93 r₄₃ = ∞ d₄₃ = 0.500 r₄₄ = ∞(imaging surface) d₄₄ = 0 0.3× 0.4× 0.5× Zoom data D5 193.324 142.89590.403 D11 3.000 43.660 80.930 D21 3.160 6.077 8.978 D28 20.516 27.62834.649 D40 11.289 11.032 16.330 Parameters of conditions Magnification:β Entrance pupil position: En 89.768 209.179 450.391 Object-to-imagedistance: L 562.991 562.991 562.991 |En|/L 0.159 0.372 0.800 Exit pupilposition: Ex −355.985 −5834.634 634.502 |Ex|/|L/β| 0.190 4.145 0.564F-number: FNO 3.500 3.789 4.037 FNO fluctuation: ΔFNO 0.537 |ΔFNO/Δβ|2.685 Object-side radius of curvature: R3f 109.670 Image-side radius ofcurvature: R3b 32.027 |(R3f + R3b)/(R3f − R3b)| 1.825

[0168] Ninth Embodiment

[0169]FIGS. 17A, 17B, and 17C show optical arrangements, developed alongthe optical axis, at magnifications of 0.3×, 0.4×, and 0.5×,respectively, of the ninth embodiment of the imaging optical systemaccording to the present invention. FIGS. 18A, 18B, and 18C showaberration characteristics in focusing at a magnification of 0.4× of theimaging optical system in the ninth embodiment.

[0170] The imaging optical system of the ninth embodiment has thevariable magnification optical system Z.

[0171] The variable magnification optical system Z comprises, in orderfrom the object side toward the image side, the first lens unit G1 withpositive refractive power, the second lens unit G2 with positiverefractive power, the third lens unit G3 with negative refractive power,the aperture stop S, and the fourth lens unit G4 with positiverefractive power.

[0172] The first lens unit G1 includes, in order from the object side,the positive meniscus lens L1 ₁″ with a concave surface directed towardthe object side, the negative meniscus lens L1 ₂′ with a concave surfacedirected toward the object side, and a positive meniscus lens L1 ₃″ witha concave surface directed toward the object side.

[0173] The second lens unit G2, in order from the object side, thenegative meniscus lens L2 ₁ with a convex surface directed toward theobject side, the biconvex lens L2 ₂, the negative meniscus lens L2 ₃with a concave surface directed toward the object side, the biconvexlens L2 ₄, and a biconvex lens L2 ₅′.

[0174] The third lens unit G3 includes the biconvex lens L3 ₁, thenegative meniscus lens L3 ₂ with a convex surface directed toward theobject side, and the negative meniscus lens L3 ₃ with a convex surfacedirected toward the object side.

[0175] The fourth lens unit G4 includes a negative meniscus lens L4 ₁″with a concave surface directed toward the object side, the positivemeniscus lens L4 ₂′ with a concave surface directed toward the objectside, the negative meniscus lens L4 ₃′ with a concave surface directedtoward the object side, the positive meniscus lens L4 ₄′ with a concavesurface directed toward the object side, the biconvex lens L4 ₅, and thebiconvex lens L4 ₆.

[0176] When the magnification is changed from 0.3× to 0.5× in focusingof the infinite object point, the first lens unit G1 is moved toward theobject side, the second lens unit G2 is moved toward the object side sothat the spacing between the first and second lens units G1 and G2 iswidened, the third lens unit G3 is moved together with the stop S towardthe object side so that the spacing between the second and third lensunits G2 and G3 is widened, and the fourth lens unit G4, after beingslightly moved once toward the image side, is slightly moved toward theobject side. Also, the object-to-image distance in the magnificationchange is kept constant.

[0177] Subsequently, numerical data of optical members constituting theimaging optical system of the ninth embodiment are shown below.Numerical data 9 Image height: 5.783 r₀ = ∞ (object) d₀ = 21.000 r₁ = ∞(object) d₁ = 26.161 r₂ = ∞ (object surface) d₂ = D2 r₃ = −153.3010 d₃ =12.000 n_(e3) = 1.48915 ν_(e3) = 70.04 r₄ = −56.0044 d₄ = 6.782 r₅ =−42.5771 d₅ = 8.000 n_(e5) = 1.61639 ν_(e5) = 44.15 r₆ = −173.4981 d₆ =15.255 r₇ = −454.5776 d₇ = 12.000 n_(e7) = 1.43985 ν_(e7) = 94.53 r₈ =−54.2450 d₈ = D8 r₉ = 74.1238 d₉ = 7.000 n_(e9) = 1.61639 ν_(e9) = 44.15r₁₀ = 47.9620 d₁₀ = 0.782 r₁₁ = 50.6461 d₁₁ = 6.639 n_(e11) = 1.43985ν_(e11) = 94.53 r₁₂ = −395.4325 d₁₂ = 2.526 r₁₃ = −67.4730 d₁₃ = 6.000n_(e13) = 1.61639 ν_(e13) = 44.15 r₁₄ = −489.0704 d₁₄ = 0.300 r₁₅ =162.7339 d₁₅ = 5.252 n_(e15) = 1.43985 ν_(e15) = 94.53 r₁₆ = −122.6735d₁₆ = 0.300 r₁₇ = 377.7299 d₁₇ = 4.142 n_(e17) = 1.43985 ν_(e17) = 94.53r₁₈ = −202.1041 d₁₈ = D18 r₁₉ = 108.3047 d₁₉ = 4.106 n_(e19) = 1.67765ν_(e19) = 31.84 r₂₀ = −192.0405 d₂₀ = 0.454 r₂₁ = 25.9085 d₂₁ = 9.623n_(e21) = 1.83945 ν_(e21) = 42.47 r₂₂ = 24.8614 d₂₂ = 2.939 r₂₃ =50.8391 d₂₃ = 2.000 n_(e23) = 1.83945 ν_(e23) = 42.47 r₂₄ = 18.5107 d₂₄= 3.223 r₂₅ = ∞ (aperture stop) d₂₅ = D25 r₂₆ = −23.8975 d₂₆ = 8.198n_(e26) = 1.61639 ν_(e26) = 44.15 r₂₇ = −142.2318 d₂₇ = 1.569 r₂₈ =−27.6769 d₂₈ = 12.000 n_(e28) = 1.43985 ν_(e28) = 94.53 r₂₉ = −15.4629d₂₉ = 0.617 r₃₀ = −15.4255 d₃₀ = 2.000 n_(e30) = 1.61639 ν_(e30) = 44.15r₃₁ = −31.9175 d₃₁ = 0.300 r₃₂ = −193.4359 d₃₂ = 5.561 n_(e32) = 1.43985ν_(e32) = 94.53 r₃₃ = −30.6965 d₃₃ = 0.300 r₃₄ = 190.3831 d₃₄ = 4.818n_(e34) = 1.43985 ν_(e34) = 94.53 r₃₅ = −61.6979 d₃₅ = 0.300 r₃₆ =63.1906 d₃₆ = 4.652 n_(e36) = 1.43985 ν_(e36) = 94.53 r₃₇ = −264.7349d₃₇ = D37 r₃₈ = ∞ d₃₈ = 33.000 n_(e38) = 1.61173 ν_(e38) = 46.30 r₃₉ = ∞d₃₉ = 13.200 n_(e39) = 1.51825 ν_(e39) = 63.93 r₄₀ = ∞ d₄₀ = 0.500 r₄₁ =∞ (imaging surface) d₄₁ = 0.000 0.3× 0.4× 0.5× Zoom data D2 131.948109.433 66.283 D8 3.000 7.576 32.565 D18 3.338 20.375 31.678 D25 6.47011.057 13.774 D37 16.892 13.207 17.349 Parameters of conditionsMagnification: β Entrance pupil position: En 104.859 165.265 302.380Object-to-image distance: L 405.147 405.147 405.147 |En|/ L 0.259 0.4080.746 Exit pupil position: Ex −368.020 2564.601 598.424 |Ex|/|L/β| 0.2732.532 0.739 F-number: FNO 3.500 3.725 3.839 FNO fluctuation: ΔFNO 0.339|ΔFNO/Δβ| 1.693 Object-side radius of curvature: R3f 108.305 Image-sideradius of curvature: R3b 18.511 |(R3f + R3b)/(R3f − R3b)| 1.412

[0178] Subsequently, parameter values of the conditions in the aboveembodiments and whether the arrangements of the embodiments satisfy therequirements of the present invention are summarized in Tables 1 through3. TABLE 1 First Second Third embodiment embodiment embodimentObject-side telecentricity|En|/L (β = 0.3) 2.71 2.62 2.96 Object-sidetelecentricity|En|/L (β = 0.4) 47.27 38.41 42.84 Object-sidetelecentricity|En|/L (β = 0.5) 2.65 2.66 2.55 Image-sidetelecentricity|En|/|L/β| (β = 0.3) 0.25 0.25 0.25 Image-sidetelecentricity|En|/|L/β| (β = 0.4) 0.54 0.69 0.84 Image-sidetelecentricity|En|/|L/β| (β = 0.5) 2.12 28.49 5.62 Conditions (1), (2) ∘∘ ∘ Conditions (1′), (2′) ∘ ∘ ∘ Conditions (1″), (2″) ∘ ∘ ∘ Differencebetween object-to-image distances at 0.3× and 0.5× 0.00000 0.000020.00000 Smallest object-side F-number, MAXFNO 3.5 3.5 3.5 |ΔFNO/Δβ| 0.490.729 0.935 Conditions (3), (4) ∘ ∘ ∘ Conditions (3′), (4′) ∘ ∘ ∘Conditions (3″), (4″) ∘ ∘ ∘ Lens arrangement of 1st lens unit; positive∘ ∘ ∘ Lens arrangement of 1st lens unit; positive, negative ∘ ∘ ∘ Lensarrangement of 1st lens unit; positive, negative, positive ∘ ∘ ∘ Virtualshape factor of 3rd lens unit 2.27 2.69 2.32 |(R3f + R3b)/(R3f − R3b)|Condition (5) ∘ ∘ ∘ Condition (5′) ∘ ∘ ∘ Condition (5″) ∘ ∘ ∘ 3rd lensunit: at least two meniscus lenses, each with a ∘ ∘ ∘ convex surfacedirected toward the object side 3rd lens unit: at least three meniscuslenses, each with ∘ ∘ ∘ a convex surface directed toward the object side

[0179] TABLE 2 Fourth Fifth Sixth embodiment embodiment embodimentObject-side telecentricity|En|/L (β = 0.3) 2.59 3.06 0.34 Object-sidetelecentricity|En|/L (β = 0.4) 11.97 58.72 0.48 Object-sidetelecentricity|En|/L (β = 0.5) 2.68 2.61 0.80 Image-sidetelecentricity|En|/|L/β| (β = 0.3) 0.25 0.26 1.47 Image-sidetelecentricity|En|/|L/β| (β = 0.4) 0.33 0.35 1.96 Image-sidetelecentricity|En|/|L/β| (β = 0.5) 0.41 0.43 2.46 Conditions (1), (2) ∘∘ ∘ Conditions (1′), (2′) x x ∘ Conditions (1″), (2″) x x x Differencebetween object-to-image distances at 0.3× and 0.5× 0.00000 0.000000.00000 Smallest object-side F-number, MAXFNO 3.45 3.5 3.5 |ΔFNO/Δβ|0.228 0.002 0.082 Conditions (3), (4) ∘ ∘ ∘ Conditions (3′), (4′) ∘ ∘ ∘Conditions (3″), (4″) ∘ ∘ ∘ Lens arrangement of 1st lens unit; positive∘ ∘ ∘ Lens arrangement of 1st lens unit; positive, negative ∘ ∘ ∘ Lensarrangement of 1st lens unit; positive, negative, positive ∘ ∘ ∘ Virtualshape factor of 3rd lens unit 2.34 2.29 2.494 |(R3f + R3b)/(R3f − R3b)|Condition (5) ∘ ∘ ∘ Condition (5′) ∘ ∘ ∘ Condition (5″) ∘ ∘ ∘ 3rd lensunit: at least two meniscus lenses, each with a ∘ ∘ ∘ convex surfacedirected toward the object side 3rd lens unit: at least three meniscuslenses, each with ∘ ∘ ∘ a convex surface directed toward the object side

[0180] TABLE 3 Seventh Eighth Ninth embodiment embodiment embodimentObject-side telecentricity|En|/L (β = 0.3) 2.60 0.16 0.26 Object-sidetelecentricity|En|/L (β = 0.4) 36.46 0.37 0.41 Object-sidetelecentricity|En|/L (β = 0.5) 2.56 0.80 0.75 Image-sidetelecentricity|En|/|L/β| (β = 0.3) 0.23 0.19 0.27 Image-sidetelecentricity|En|/|L/β| (β = 0.4) 0.76 4.15 2.53 Image-sidetelecentricity|En|/|L/β| (β = 0.5) 13.92 0.56 0.74 Conditions (1), (2) ∘∘ ∘ Conditions (1′), (2′) ∘ x x Conditions (1″), (2″) ∘ x x Differencebetween object-to-image distances at 0.3× and 0.5× 0.00000 0.000000.00000 Smallest object-side F-number, MAXFNO 3.51 3.5 3.5 |ΔFNO/Δβ|0.304 2.685 1.693 Conditions (3), (4) ∘ ∘ ∘ Conditions (3′), (4′) ∘ ∘ ∘Conditions (3″), (4″) ∘ x x Lens arrangement of 1st lens unit; positive∘ ∘ ∘ Lens arrangement of 1st lens unit; positive, negative ∘ ∘ ∘ Lensarrangement of 1st lens unit; positive, negative, positive ∘ ∘ ∘ Virtualshape factor of 3rd lens unit 2.69 1.83 1.41 |(R3f + R3b)/(R3f − R3b)|Condition (5) ∘ ∘ ∘ Condition (5′) ∘ ∘ ∘ Condition (5″) ∘ x x 3rd lensunit: at least two meniscus lenses, each with a ∘ ∘ ∘ convex surfacedirected toward the object side 3rd lens unit: at least three meniscuslenses, each with ∘ x x a convex surface directed toward the object side

[0181] The imaging optical system of the present invention describedabove can be used in an optical apparatus such as a motion picture filmscanner (a telecine apparatus) or a height measuring apparatus.Embodiments of such apparatuses are described below.

[0182]FIG. 19 shows an embodiment of the telecine apparatus using theimaging optical system of the present invention. This telecine apparatusincludes a light source 11 for projecting a motion picture, a motionpicture film 14 wound on reels 12 and 13, an imaging optical system 15,such as that disclosed by each embodiment in the present invention, anda CCD camera 16. In the figure, the specific arrangement of the imagingoptical system 15 is omitted.

[0183] In the telecine apparatus of this embodiment constructed asmentioned above, light emitted from the light source 11 is projected onthe motion picture film 14, and projected light is imaged by the CCDcamera 16 through the imaging optical system 15. In the imaging opticalsystem 15, the magnification can be changed so that the imageinformation of the motion picture film 14 is imaged over the entireimaging area of the CCD camera 16 in accordance with the size of themotion picture film 14.

[0184] According to the telecine apparatus of the embodiment, theimaging optical system 15 is both-side telecentric so that even when theimaging magnification is changed, the conjugate length remainsunchanged. Therefore, there is no need to adjust the positions ofindividual members. Since the fluctuation of the image-side F-number isminimized and a loss of the amount of light is reduced, the adjustmentof brightness is unnecessary. Moreover, a change in magnification on animage plane, caused by the disturbance of flatness of an object to bephotographed, such as the film, can be kept to a minimum.

[0185]FIG. 20 shows an embodiment of the height measuring apparatususing the imaging optical system of the present invention. In thisembodiment, the imaging optical system is used as a confocal opticalsystem.

[0186] The height measuring apparatus of the embodiment includes a lightsource 21, a polarization beam splitter 22, a disk 23 provided with aplurality of pinholes, a quarter-wave plate 24, a confocal opticalsystem 25 constructed like the imaging optical system disclosed by eachembodiment in the present invention, an XYZ stage 26, an imaging lens27, an image sensor 28, a motor 29 driving the disk 23, a stage drivingmechanism 30 driving the XYZ stage 26, a sensor driving mechanism 31driving the image sensor 28, and a computer 32 controlling the drive ofthe motor 29, the stage driving mechanism 30, and the sensor drivingmechanism 31.

[0187] In the height measuring apparatus of the embodiment constructedas mentioned above, a p or s component of linear polarization, of lightemitted from the light source 21, is reflected by the polarization beamsplitter 22, passes through the pinhole provided on the disk 23, andsuffers a phase shift of 45° through the quarter-wave plate 24 toirradiate a certain point of a specimen 33 placed on the XYZ stage 26through the confocal optical system 25. Light reflected by the specimen33 passes through the confocal optical system 25, suffers a phase shiftof 45° through the quarter-wave plate 24, passes through the spot on thedisk 23, is transmitted through the polarization beam splitter 22, andis imaged by the image sensor 28 through the imaging lens 27. By drivingthe motor 29 through the computer 32, the entire surface of the specimen33 can be scanned. In this case, the position where the intensity oflight of a confocal image of the specimen 33 imaged by the image sensor28 becomes ultimate is found while shifting the driving mechanism 30 or31 along the optical axis. Whereby, the height of the specimen isdetected.

[0188] The magnification of the confocal optical system 25 can also bechanged in accordance with the size of the specimen 33.

[0189] In this height measuring apparatus also, the confocal opticalsystem 25 is both-side telecentric so that even when the magnificationis changed, the conjugate length remains unchanged. Therefore, there isno need to adjust the positions of individual members. Since thefluctuation of the image-side F-number is minimized and a loss of theamount of light is reduced, the adjustment of brightness is unnecessary.

What is claimed is:
 1. An imaging optical system including a variablemagnification optical system, the variable magnification optical systemcomprising, in order from an object side toward an image side: a firstlens unit with positive refractive power; a second lens unit withpositive refractive power; a third lens unit with negative refractivepower; a fourth lens unit with positive refractive power, and anaperture stop interposed between the third lens unit and the fourth lensunit, wherein the variable magnification optical system changes animaging magnification while keeping a distance between an object and animage constant in the imaging optical system, the imaging magnificationis changed by varying spacing between the first lens unit and the secondlens unit, spacing between the second lens unit and the third lens unit,and spacing between the third lens unit and the fourth lens unit, andwhen the imaging magnification is changed, the imaging optical systemsatisfies the following conditions in at least one variablemagnification state: |En|/L>0.4 |Ex|L1/β|>0.4 where En is a distancefrom a first lens surface on the object side of the variablemagnification optical system to an entrance pupil of the imaging opticalsystem, L is the distance between the object and the image in theimaging optical system, Ex is a distance from a most image-side lenssurface of the variable magnification optical system to an exit pupil ofthe imaging optical system, and β is a magnification of an entire systemof the imaging optical system.
 2. An imaging optical system according toclaim 1, further satisfying the following conditions: 1.0<MAXFNO<8.0|ΔFNO/Δβ<5 where MAXFNO is a smallest object-side F-number where theimaging magnification of the imaging optical system is changed, ΔFNO isa difference between the object-side F-number at a minimum magnificationand the object-side F-number at a maximum magnification in the entiresystem of the imaging optical system, and Δβ is a difference between theminimum magnification and the maximum magnification in the entire systemof the imaging optical system.
 3. An imaging optical system according toclaim 1, further satisfying the following condition:0.6<|(R3f+R3b)/(R3f−R3b)|<5.0 where R3f is a radius of curvature of amost object-side surface of the third lens unit and R3b is a radius ofcurvature of a most image-side surface of the third lens unit.
 4. Animaging optical system according to claim 1, wherein a most object-sidelens of the first lens unit has positive refractive power.
 5. An imagingoptical system according to claim 1, wherein the first lens unitincludes, in order from the object side, a lens with positive refractivepower, a lens with negative refractive power, and a lens with positiverefractive power.
 6. An imaging optical system according to claim 1,wherein the third lens unit includes at least two meniscus lenses, eachwith a convex surface directed toward the object side.
 7. An imagingoptical system according to claim 1, wherein the third lens unitincludes two meniscus lenses, each with negative refractive power, andone meniscus lens with positive refractive power.
 8. An opticalapparatus having an imaging optical system, the imaging optical systemincluding a variable magnification optical system, the variablemagnification optical system comprising, in order from an object sidetoward an image side: a first lens unit with positive refractive power;a second lens unit with positive refractive power; a third lens unitwith negative refractive power; a fourth lens unit with positiverefractive power, and an aperture stop interposed between the third lensunit and the fourth lens unit, wherein the variable magnificationoptical system changes an imaging magnification while keeping a distancebetween an object and an image constant in the imaging optical system,the imaging magnification is changed by varying spacing between thefirst lens unit and the second lens unit, spacing between the secondlens unit and the third lens unit, and spacing between the third lensunit and the fourth lens unit, and when the imaging magnification ischanged, the imaging optical system satisfies the following conditionsin at least one variable magnification state: |En|/L>0.4 |Ex|/|L/β|>0.4where En is a distance from a first lens surface on the object side ofthe variable magnification optical system to an entrance pupil of theimaging optical system, L is the distance between the object and theimage in the imaging optical system, Ex is a distance from a mostimage-side lens surface of the variable magnification optical system toan exit pupil of the imaging optical system, and β is a magnification ofan entire system of the imaging optical system.